An individual's relevant health information is stored in multiple, independent sources (Institute of Medicine 2001). Therefore not all the clinical information useful to providers is available during a patient encounter, meaning decisions frequently occur with incomplete medical knowledge (Kalra 2004). Health information exchange (HIE), the automated sharing of individuals'clinical information across organizations, holds the promise of quality improvements and cost savings. Specifically relevant to the continuing care of patients with chronic conditions, HIE has the potential to improve efficiency and timeliness by reducing redundancy of diagnostic testing. Additionally, the lack of access to information stored by other organizations can be a barrier to effective coordination of care between multiple providers (Casalino, Gillies et al. 2003). Efforts at establishing systems of HIE are widespread and advocated by the federal government (Walker, Pan et al. 2005). However, we currently do not know how these systems are actually used by health professionals (Ash and Guappone 2007). This proposal applies knowledge from previous research on information seeking behavior and organizational technology usage in order to understand health information exchange usage in the context of a healthcare encounter. The specific aim of this proposal is to examine which patient characteristics (like chronic conditions) are associated with system usage. In addition, since healthcare occurs within an organization, those characteristics contribute to the usage of the system by individuals. Hypotheses will be empirically examined by combining secondary data on patients in a HIE serving the medically indigent in Central Texas with primary surveys of the organizations participating in the system. This system provides a unique opportunity by providing both data on the patients and on the usage history of those providers who utilize the system. Data on the latter come in the form of system usage logs. This proposal will model the actual usage of the HIE during approximately 612,000 healthcare encounters occurring in 2007-2008 to determine the factors associated with system usage. The identification of the factors determining and affecting HIE usage will be useful to both local organizations working with, or beginning, HIE systems and to national policy makers. Understanding how HIE systems are actually used is particularly relevant to the continuing care of patients with chronic conditions, like cancer and mental illness, who require an effective coordination of care between multiple providers, have many medications and different laboratory tests. PUBLIC HEALTH RELEVANCE: One reason the health care system fails to deliver efficient, timely and safe care is individuals'clinical relevant information is stored in multiple, independent sources. Health information exchange is a national goal, currently implemented in many locations, and promises huge financial and quality improvements. However, how these systems are actually used is not exactly known, and therefore a needed area of research.